In recent years, technologies advance and cause a fast development for various different products, particularly the electronic, information, and communication products. These products not only come with innovative designs, structures and functions, but also meet the requirements for user-friendly application and input method as well as providing diversified features. The development of a touch panel has changed the input mode of the traditional electronic products, so that users are no longer restricted by a traditional input device (such as a press key or a mouse for inputting data or operating instructions.) A user just needs to use the user-friendly input interface of a touch panel and follows the functional icon on a screen to click the desired function and instruction directly by a finger or a touch pen to execute a task without going through special training and learning. At present, touch panels are used extensively in different personal electronic products such as a palm-sized PC, a personal digital assistant (PDA), and an information appliance, and these products are used in public information stations for the medical treatment, traffic, travel and education related area, such that the scope of applicability and the market requirements of the touch panels tend to be expanded continuously.
In general, a touch panel installs an ITO film onto a transparent glass substrate to form an ITO glass that generally operates together with a flat cable and a circuit board, and a control IC installed on the circuit board executes a control instruction according to the corresponding position pressed by a user, so as to achieve the purpose of inputting data and instruction through the touch panel. Since these touch panels are commonly installed for various different electronic products as a liquid crystal display (LCD), therefore users can press the touch panel to input data and instruction without requiring to install traditional input devices (including a keyboard and a mouse) in order to save more working space or install a larger display panel to facilitate users to browse or input data.
In view of the description above, the ITO glass is a major component of the touch panel, and the ITO glass comprises a transparent glass substrate and a transparent conducting layer. In the fabrication of an ITO glass, an electrically insulating transparent glass substrate is coated with a layer of transparent conducting metal material, and the transparent conducting layer is formed on the transparent glass substrate. In general, the transparent conducting layer is made of indium tin oxide (ITO) and the transparent conducting layer is comprised of a plurality of ITO transparent electrodes disposed in the transparent glass substrate. Referring to FIG. 1 for a detailed description of the structure of the ITO glass, the manufacturing process of the ITO glass is described as follows:
(101) Rinsing: Before the transparent glass substrate is manufactured, it is necessary to rinse the surface of the transparent glass substrate to remove any dust and particle attached on the transparent glass substrate.
(Step 102) Coating: An indium tin oxide film is coated onto a lateral surface of the transparent glass substrate;
(Step 103) Coating a photoresist (P/R) layer: A layer of photoresist material is coated onto the transparent glass substrate having the indium tin oxide film by roller printing.
(Step 104) Prebake: The transparent glass substrate is heated slowly to coat and fix the photoresist layer onto the transparent glass substrate and prepare for the following processes.
(Step 105) Exposure: A fixed amount of ultraviolet (UV) light is projected onto the photoresist layer of the transparent glass substrate for a chemical reaction with the photoresist layer to form a masked pattern area and an exposed area on the photoresist layer.
(Step 106) Development: The exposed area is cleaned by a developer to wash away the photoresist layer in the exposed area in order to expose the indium tin oxide film.
(Step 107) Etching: The indium tin oxide film exposed from the exposed area is rinsed by royal water.
(Step 108) Stripping: An alkaline solution, preferably sodium hydroxide (KOH), is used for rinsing the masked pattern area to dissolve the photoresist layer on the masked pattern area, so that the required ITO transparent electrodes can be formed on the transparent glass substrate.
(Step 109) After-etch Inspection: The electrodes of the transparent glass substrate are inspected. If there is any short circuit found between the ITO electrodes, then the point of short circuit will be removed by a laser correction machine, so as to complete the fabrication of the ITO glass and prepare for the later process to install the transparent glass substrate into the touch panel.
When the ITO glass is used as an LCD display, users often observe a discontinuous layer, a blurred image, a particle formation or a reduced resolution of the display screen through the ITO glass, since the refractive index of the light at each position of the ITO glass is different. Referring to FIG. 2 for the ITO glass 1 produced by the foregoing process, the ITO glass 1 comprises a transparent glass substrate 10 and a plurality of ITO transparent electrodes 12 disposed on the transparent glass substrate. The refractive index of light at the positions of the transparent glass substrate 10 without the ITO transparent electrodes 12 ranges between 1.4 and 1.5, and the refractive index of light of the ITO transparent electrodes 12 ranges from 1.8 to 2.2. Since the refractive indexes of the two are different, the image quality of the screen observed by users will be lowered greatly, and the images of smaller graphics and texts will become blurred, and thus users may not be able to successfully press the correct pressing positions to execute a control instruction corresponding to the pressing position, and thus users cannot input their desired data or instruction successfully.